Clouds 101 Special: Kelvin-Helmholtz Clouds

This time I have a truly interesting cloud type on my repertoir. These wave clouds are certainly something we would imagine in a Sci-Fi scene, to be formations from another planet (indeed they can be seen on ther planets and I will show you that as well). These are the famous Kelvin-Helmholtz clouds and are named after Lord Kelvin and Hermann von Helmholtz.

These clouds are also known as billow clouds, shear-gravity clouds and KHI clouds and are produced in specific conditions. These clouds are formed between two layers of air, with different densities, traveling at different speeds. The upper layers of air are moving at higher speeds and will often scoop the top of the cloud layer into these wave-like rolling structures.

The stable lower air being lifted, cooled, and condensed so that this process becomes visible, though this commonly happens many places without being visible. These clouds often form on windy days where there is a difference in densities of the air, such as in a temperature inversion. Therefore, if a warm, less dense layer exists over a layer of colder, denser air, and the wind shear across the two layers is strong enough, eddies will develop along the boundary. The rolling eddies seen at the top of the cloud layers are usually evenly spaced and easily identifiable.

These clouds are often good indicators of atmospheric instability and the presence of turbulence for aircraft. However, if the air layers are traveling at the same speed, such waves will not occur. And as I mentioned before, the same phenomenon occurs on other planets. Here is a picture of Kelvin-Helmholtz clouds on Saturn.